- Industry: Weather
- Number of terms: 60695
- Number of blossaries: 0
- Company Profile:
The American Meteorological Society promotes the development and dissemination of information and education on the atmospheric and related oceanic and hydrologic sciences and the advancement of their professional applications. Founded in 1919, AMS has a membership of more than 14,000 professionals, ...
The intense luminosity that propagates upward from earth to cloud base in the last phase of each lightning stroke of a cloud-to-ground discharge. In a typical flash, the first return stroke ascends as soon as the descending stepped leader makes electrical contact with the earth, often aided by short ascending ground streamers. The second and all subsequent return strokes differ only in that they are initiated by a dart leader and not a stepped leader. It is the return stroke that produces almost all of the luminosity and charge transfer in most cloud-to-ground strokes. Its great speed of ascent (about 1 × 10<sup>8</sup> m s<sup>−1</sup>) is made possible by residual ionization of the lightning channel remaining from passage of the immediately preceding leader, and this speed is enhanced by the convergent nature of the electric field in which channel electrons are drawn down toward the ascending tip in the region of the streamer's electron avalanche. Current peaks as high as 3 × 10<sup>5</sup> A have been reported, and values of 3 × 10<sup>4</sup> A are fairly typical. The entire process of the return stroke is completed in a few tens of microseconds, and even most of this is spent in a long decay period following an early rapid rise to full current value in only a few microseconds. Both the current and propagation speed decrease with height. In negative cloud-to-ground flashes the return stroke deposits the positive charge of several coulombs on the preceding negative leader channel, thus charging earth negatively. In positive cloud-to-ground flashes, the return stroke deposits the negative charge of several tens of coulombs on the preceding positive leader channel, thus increasing positive charge on the ground. In negative cloud-to-ground flashes, multiple return strokes are common. Positive cloud-to-ground flashes, in contrast, typically have only one return stroke. The return streamer of cloud-to-ground discharges is so intense because of the high electrical conductivity of the ground, and hence this type of streamer is not to be found in air discharges, cloud discharges, or cloud-to-cloud discharges.
Industry:Weather
The intensity of a pixel, usually an integer. For grayscale images, the pixel value is typically an 8-bit data value (with a range of 0 to 255) or a 16-bit data value (with a range of 0 to 65535). For color images, there are 8-bit, 16-bit, 24- bit, and 30-bit colors. The 24-bit colors are known as true colors and consist of three 8-bit pixels, one each for red, green, and blue intensity.
Industry:Weather
The intensely bright portion of the sun (or any other star) visible to the unaided eye. Although the sun appears to have a surface, the photosphere is actually a gaseous layer many hundreds of kilometers thick from which the light is emitted.
Industry:Weather
The instability associated with a supercooled or supersaturated phase of matter. A small fluctuation (on a molecular scale) or foreign particle may cause change to a more stable phase. For example, at a temperature below the equilibrium melting point of ice, the ice phase is stable, whereas liquid water is supercooled and is unstable because its chemical potential is higher than that of ice. A small fluctuation such as collision with ice may cause the supercooled water to change into ice.
Industry:Weather
The initial leader of a lightning discharge; an intermittently advancing column of high ionization and charge that establishes the channel for a first return stroke. The peculiar characteristic of this type of leader is its stepwise growth at intervals of about 50– 100 μs. The velocity of growth during the brief intervals of advance, each only about 1 μs in duration, is quite high (about 5 × 10<sup>7</sup> m s<sup>−1</sup>), but the long stationary phases reduce its effective speed to only about 5 × 10<sup>5</sup> m s<sup>−1</sup>. To help explain its mode of advance, the concept of a pilot streamer was originally suggested, but has been supplanted by analogy to recent work on long laboratory sparks.
Industry:Weather
The indefinite belts in each hemisphere between the regions of tropical and temperate climates. The polar boundaries are considered to be roughly 35°N and 35°S latitudes, but vary greatly according to continental influence, being farther poleward on the west coasts of continents and farther equatorward on the east coasts.
Industry:Weather
The hypothetical area normal to the incident radiation that would geometrically intercept the total amount of radiation actually scattered by a scattering particle.
Industry:Weather
The hypothetical climate that would prevail on a uniform solid earth with no atmosphere. Thus, it is a climate of temperature alone and is determined only by the amount of solar radiation received, that is, determined by the elevation of the sun as it varies with season. Solar climatic zones, therefore, are parallel to lines of latitude. The solar climate and the nearly synonymous mathematical climate have both grown out of the earliest approach to climatology, as is indicated by the fact that “climate” takes its name from the inclination (Greek ''klima'') of the sun's rays.
Industry:Weather
The increase in wind speed above the top of a hill due to the Bernoulli effect.
Industry:Weather
The increase in the wave height of wind waves in shallow water because of the divergence in wave group velocity. This happens when the depth decreases near the coast.
Industry:Weather
